Modern Alchemy: Mercury into Gold?
A San Francisco-based fusion startup, Marathon Fusion, has announced a remarkable achievement: the transmutation of mercury into stable gold using neutrons generated from fusion reactions. The company claims its experimental rate of mercury-to-gold conversion is ten times greater than the record set by CERN in 2025.
Beyond the headline-grabbing prospect of modern-day alchemy, Marathon Fusion's broader ambition is to leverage this technology for the production of scarce medical isotopes, crucial for cancer diagnosis and treatment, while simultaneously advancing the engineering capabilities required for future fusion power plants.
How Nuclear Transmutation Works
Unlike chemical reactions that rearrange atoms, nuclear transmutation fundamentally alters an atom's nucleus, resulting in a different element or isotope. Marathon Fusion's proposed method involves starting with mercury-198, a naturally occurring stable isotope. High-energy neutrons generated by a deuterium-tritium fusion reaction strike these nuclei, ejecting two neutrons and producing mercury-197. This mercury-197 is radioactive and subsequently decays through electron capture into stable gold-197.
While the underlying nuclear physics is well-established – scientists have previously produced gold in particle-physics experiments, including at CERN's Large Hadron Collider – the challenge lies in producing meaningful quantities economically. For context, CERN's ALICE experiment reportedly generated only about 29 picograms of gold over four years.
Validation and Industrial Scale Challenges
Marathon Fusion's latest claim, shared via social media, asserts an experimental breakthrough, moving beyond its 2025 research paper which described a proposed production method supported by nuclear simulations. The company has shared energy-spectrum plots indicating the presence of specific isotopes, including copper-64 and copper-67 from zinc irradiation, and mercury-197 and gold-197 signatures related to the mercury-to-gold process.
However, these plots alone do not establish the total quantity of gold produced, its purity, the efficiency of the process, or its commercial scalability. Independent scientific validation of these experimental results is essential to confirm their scale and significance.
Focus on Medical Isotopes
While gold production captures public imagination, Marathon Fusion emphasizes that medical isotopes offer a more immediate and practical application for its technology. Radioisotopes are vital in nuclear medicine for diagnosing diseases, imaging tumors, and delivering targeted radiation to cancer cells.
Marathon Fusion claims to have already begun producing radioactive copper isotopes by irradiating zinc with fusion-generated neutrons. Copper-64 is used in diagnostic imaging, while copper-67 is being explored for targeted radionuclide therapy. The company posits that fusion reactors could provide a critical additional source of medical isotopes as demand continues to grow.
Building a Fusion Reactor in San Francisco
The startup's immediate objective is not primarily electricity generation, but to produce neutrons at sufficiently high rates and concentrations for industrial applications like manufacturing medical isotopes and potentially gold. Marathon Fusion aims to direct a trillion neutrons per second at a 1 cm target continuously for years, with ambitious plans to double its reactor's power density monthly.
Achieving a successful fusion reaction is distinct from establishing a commercially viable fusion power plant. Significant engineering hurdles remain, including demonstrating sustained operation, reliable equipment, efficient energy conversion, fuel-cycle management, materials durability, and competitive costs. A 2026 analysis by Harvard's Belfer Center cautioned against assuming imminent commercial deployment of fusion technology despite recent advances.
Economic Impact: Lab-Grown Gold?
The prospect of artificially produced gold has drawn comparisons to lab-grown diamonds, which have impacted the diamond market's economics. However, nuclear transmutation is a far more complex and energy-intensive process than the chemical vapor deposition or high-pressure, high-temperature methods used to create lab-grown diamonds.
Marathon's 2025 paper estimated that a suitably designed fusion plant could potentially produce around two tonnes of gold annually per gigawatt of thermal power, or thousands of kilograms per year at gigawatt scale. These are modeled projections, not demonstrated commercial outputs. The actual impact on gold prices would depend on fusion economics, production costs, management of radioactive byproducts, and global market supply dynamics. The possibility of lower-cost gold remains conditional on overcoming several difficult engineering and economic challenges first.